Stabilized light-sensitive intermediate sheet

ABSTRACT

Light-sensitive intermediate sheet is stabilized against atmospherically induced deterioration by including in said intermediate sheet a normally non-volatile organic aromatic amine preservative.

United States Patent [191 Meyer et 211. Y

[4 1 Nov. 6, 1973 STABILIZED LIGHT-SENSITIVE INTERMEDIATE SHEET Inventors: Leo A. Meyer, St. Paul; Robert J.

Perkins, White Bear Lake, both of Minn.

Assignee: Minnesota Mining and Manufacturing Company, St. Paul, Minn.

Filed: Oct. 15, 1971 Appl. No.: 189,752

US. Cl 96/82, 96/67, 96/88,

96/114.1,117/36 .8 Int. Cl G03c l/92 Field of Search 96/114.1, 67, 82,

Primary ExaminerNorman G. Torchin Assistant ExaminerEdward C. Kimlin Attorney-Kinney, Alexander, Sell, Steldt & Delahunt [57] ABSTRACT Light-sensitive intermediate sheet is stabilized against I atmo s'pherically induced deterioration by including in said intermediateshe'et a normally non-volatile organic aromatic amine preservative.

9 Claims, N0 Drawings inter-reactive copy sheet.

STABILIZED LIGHT-SENSITIVE INTERMEDIATE SHEET FIELD OF THE INVENTION BACKGROUND OF THE INVENTION:

As described in U.S. Pat. No. 3,094,417 and in copending application Ser. No. 180,215, filed Sept. 13,

1971, both of which are incorporated herein by refer: I

ence, copies of graphic originals may be made by first exposing to light a light-sensitive intermediate sheet while in reflex position against the original, and then heating the intermediate sheet while in contact with an A preferred form of light-desensitizable intermediate sheet employs (1) a volatilizable alpha-naphthol, e.g., 4-methoxy-1- naphthol, as the acceptor which is reactive with a coreactant to provide a visible change and is rendered non-reactive with said co-reactant upon desensitization with excited oxygen, (2) an oxygen-sensitizing polycyclic aromatic dye, and (3) a film-forming polymeric binder, e.g., ethyl cellulose, in which the acceptor and dye are dispersed and coated on thin translucent paper or transparent film, all as described in copending application Ser. No. 180,215 filed Sept. 13, 1971.

The highly sensitive intermediate sheet, as ordinarily stored in a protective wrapping or sealed envelope and enclosed within a light-tight box or outerwrapping, is stable under prolonged storage. It was found with'the intermediate sheet of the type described in U.S. Pat.-

to produce unevenor partially obscured copies. Afterseveral days, the edges of the intermediate sheet 'rnaterial are no longer light-sensitive, and this condition gradually worsens until wide margins along each exposed edge are no longer useful. The deteriorated areas may be recognized by the appearance of a blue discoloration on the intermediate sheet and a darkening along corresponding edge areas of the resulting copy.

Although the light-sensitive intermediate sheet mateloss of sensitivity. As a result, the intermediate sheet material in stack or roll form may be left exposed to the atmosphere in automatic copying machines until entirely consumed, without any necessity for discarding the outer layers and without obtaining background darkening of copy edge areas.

SCHEDULE A The construction of the light-sensitive intermediate sheet material which is stabilized according to the present invention comprises a layer of film-forming binder having dispersed therethrough a reactant or acceptor and certain polycyclic, aromatic, oxygen-sensitizing dyes. The reactant or acceptor can be defined as a photosens'itivematerial which is capable of being readily desensitized by excited molecular oxygen and which will react with a co-reactant to produce a distinctly visiwith a suitable heat-sensitive receptor sheet containing a co-reactant to make a copy of the original or it can be illuminated with black (ultraviolet) light to produce a fluorescent image on the imaging sheet itself if the acceptor exhibits strong visible fluorescence with its major absorption bands preferably being in the ultraviolet region. The co-reactantfor the acceptors which exhibit strong visible fluorescence comprises photons of the proper energy necessary to excite the fluorescent acceptor, i.e., photons of ultraviolet light in the wavelength range of 200-400 nanometers.

Although the intermediate sheets do not require the presence of a separate supporting backing, these sheets are typically provided with film material backings (e.g.,

rial utilizing certain oxygen-sensitizing polycyclic aromatic dyes, described in co-pending application Ser. No. 180,215 filed Sept. 13, 1971, exhibits considerably less atmospheric deterioration than the intermediate sheet material described in U.S. Pat. No. 3,094,417, it has now been found possible to virtually eliminate the atmospheric deterioration of the intermediate sheet material which utilizes the oxygen-sensitizing polycyclic aromatic dyes. The intermediate sheet material is stabilized by including in the light-sensitive layer a normally nonvolatile organic aromatic amine preservative which is essentially non-reactive with the remaining components of said layer. The stabilized light-sensitive intermediate sheet material may be exposed to the atmosphere for days or weeks without any observable Mylar polyester, gassine paper and the like). When intermediate sheets are desired, the backing is normally a thin, light-transmissive, transparent, flexible film or paper and the film-forming binder, acceptor and sensitizing dye are in the form of a thin face-coating bonded to the flexible film or paper.

The photosensitive reactants or acceptors which can be used in the intermediate sheets can be of many and various types. For example, alpha-naphthols are quite useful, e.g., 4-methoxy-1-naphthol, l-hydroxy-2- methyl-4-methoxy naphthalene, l-hydroxy-4-ethoxy naphthalene, binaphthyl, 1,1-dihydroxy-2,2'-binaphthyl, 1,4- dihydroxy naphthalene, 1,3-dihydroxy naphthalene, 1,5-dihydroxynaphthalene with acetone or with adipolyl chloride. Generally, these alpha-naphthol photosensitive reactants can be described as an alpha-naphthol having attached directly to the 'hydroxy-substituted aromatic ring a preponderance of electron donor groups which may be alkyl, aryl, alkoxy, aryloxy, hydroxy or amino.

Another useful class of photosensitive reactants or acceptors are those substituted hydrazones in which the amino group is either unsubstituted or is substituted with electron-donating groups such as aryl or alkyl radicals. Representative reactants in this class include the phenylhydrazones, simple hydrazones, and N,N-dimethylhydrazones.

Another large class of useful photosensitive reactants or acceptors comprises those compounds possessing a diene unsaturation which are capable of reacting in a Diels-Alder reaction with typical dienophiles such as maleic anhydride. Typical examples of these compounds are furan, difurfuryldithiooxamide, and 1,3- diphenylisobenezofuran.

Olefins substituted with sufficient electron-donating groups to make them photosensitive are also useful in the imaging sheets described herein. Typical examples of such olefins include tetramethylethylene, enamines, and tetramethoxyethylene.

Other photosensitive reactants or acceptors include substituted oxazoles and substituted imidazoles, e.g., 2,5-diphenyloxazole, 2-( lnaphthyl)-5-phenyloxazole, and triphenylimidazole. Other useful acceptors known in the art can also be used, e.g., substituted dithiooxamides.

Photosensitive reactants or acceptors which exhibit strong fluorescence under ultraviolet light include 2,5- diphenyloxazole, 2-(lnaphthyl)-5-phenyloxazole, and 1,3-diphenylisobenzofuran. Other such acceptors are known in the art.

The oxygen-sensitizing dyesuseful in the practice of this invention can be described as polycyclic aromatic compounds comprising at least two moieties in conjugate relationship as part of a single chromophore, each said moeity comprising three linearly kata condensed six-membered aromatic rings, an -OZ group being attached to the meso position of such said moiety, wherein Z is a stable, monovalent radical; said OZ group being a solubilizing group for said compound; wherein at least one auxochromic group comprising an atom having an atomic weight of at least 31 is bonded to said chromophore, said atom being attached directly Although the OZ and OZ groups which are present on the dye compounds are also auxochromic Generally, it may be said, that -Z and Z are monov'alent radicals which are stable under ambient conditions and which do not cause decomposition of the chromophore portion of the dye compound. That is,these radicals do not oxidize or reduce the chromophore portion of the dye compound nor do they destroy or adversely affect the effectiveness of the compound as a dye. Within these limitations the -OZ and OZ radicals can be stable derivatives of an inorganic acid, e.g., OSO *where Y is an alkali metal, alkaline earth metal, or ammonium ion; OPO R where R is hydrogen or a stable organic radical; and -OPO R where R is hydrogen or a stable organic radical.

Insofar as organic radicals are concerned, Z and ,Z' may be alkyL cy'cloalkyl, substituted alkyl and cycloalkyl, alkenyl, alkynyl, aryl, polycyclic, acyl, alkaryl or aralkyl. Z and Z may be the same or different. Alkyl to said chromophore. The above-mentioned moietie'scomprising three linearly kata condensed sixmembered aromatic rings may be described pictorially as follows:

and

The aromatic rings may be homocyclic (carbon atoms) or heterocyclic, the hetero atoms being generally nitrogen. Of course, a single compound can contain both homocyclic and heterocyclic moieties of the type just described, or the compound may contain only homocyclic or only heterocyclic moieties.

These moieties are in conjugate relationship in the compound. Thus, the moieties may be bonded together in peri fashion such thatthe two moieties share atoms, or the moieties may be attached to each other in conjugate relationship through at least one linking moiety, where the linking moiety is selected from the group consisting of (a) atoms which are at least trivalent and are capable of forming convalent bonds, (b) ligands, having two or more atoms, which are at least bidentate, and (c) covalent single or double bonds.

Additionally, these dye compounds have at least one auxochromic group bonded to the chromophore thereof, the auxochromic group comprising a heavy atom, i.e., an atom having an atomic weight of at least 31. The preferred auxochromic groups consist only of a single heavy atom.

radicals having one carbon or more are common Z radicals, and lower alkyl radicals are preferred, although long chain alkyls are also useful. Substituted alkyl radicals are herein defined to include alkyl radicals which are substituted with any moiety or group other than hydrogen atoms and other alkyl radicals.

The rnoieties comprising the. three kata condensed six-membered aromatic rings are in a conjugate relationship in the dye compounds so that these moieties are part of a single chromophore (i.e., part of the same chromophore). A chromophore may be defined as a group of atoms or electrons in a molecule which is chiefly responsible for an absorption band, as defined in Theory and Application of Ultraviolet Spectroscopy; Jaffe and Orchin; John Wiley & Sons, Inc. (1962), incorporated herein by reference. The two moieties may be bonded or condensed together in peri fashion, e.g.,

where the two moieties share atoms, or the moieties may be attached to each other in conjugate relationship through at least one linking moeity. The linking moi- The size, chemical nature or structure of the linking moiety is not critical insofar as the general ability of the dye compound to function as an oxygen sensitizer is concerned, so long as the two moieties comprising the kata condensed aromatic rings are attached to each other in conjugate relationship such that they are part of a single chromophore.

The linking moiety, of course, can be a polycyclic structure (homocyclic or heterocyclic). Hetero atoms in the heterocyclic linking moieties are generally nitrogen, oxygen and sulfur.

In many of the compounds there are two linking moieties. For example, there may be two ligands, one ligand and a covalent bond, two covalent bonds, etc., as linking moieties in a single compound.

The auxochromic groups which are bonded to the chromophore portion of the dye compound may con? sist of one atom or of many atoms, so long as a heavy atom (i.e. having an atomic weight of at least 31), present as part of the auxochromic group, is bonded'directly to the chromophore portion of the dye. An auxochromic group may be defined as a group bonded to a chromophore which influences the nature of the excited states, as defined in Theory and Application of Ultraviolet Spectroscopy; J affee and Orchin; John Wiley & Sons, Inc. (1962).

Preferred single atom auxochromic groups include chlorine, bromine, mercury, sulfur, iodine and selenium. Other useful single atom auxochromic groups include phosphorus (treated herein as having an atomic weight of 31), arsenic, tellurium, germanium, tin, lead and antimony. The auxochromic group may consist of more than one atom so long as a heavy atom present as part of the auxochromic group is directly bonded to the chromophore portion of the dye. For example,

are useful auxochromic groups.

The above-described auxochromic groups may be bonded directly to one or both of the moieties comprising the kata condensed aromatic rings, or the auxochromic groups may be bonded to the linking moiety instead, so longas the auxochromic'groups are'bonded to the chromophore portion of the compound. So far as is known, the particular positions of attachment of the auxochromic groups to the chromophore do not influence the ability of the dye compound to function as an oxygen sensitizer.

Although not all dye compounds coming within the foregoing description are useful as oxygen-sensitizers in the practice of this invention, a suitable test has been found which accurately and conveniently distinguishes useful polycyclic aromatic dyes of the above description from those dyes which are not suitable for use in this invention. A particular dye to be tested is first dissolved in an inert organic solvent selected from the group consisting of chloroform, acetone and ethanol, or mixtures thereof, at a concentration of 0.001 moles per liter. At ambient temperature, the dye solution (100 milliliters in a a 200 milliliter open top beaker) is directly exposed to ultraviolet light in the 200-400 nanometer wavelength range using 70 watt (Spectroline Black Light, Model No. TF-250) black light at a distance of about 6-8 inches, whereupon visible fluorescence is instantaneously observed for solutions of dyes which are useful in the practice of this invention. When the dye solutions are exposed and observed in the absence of visible light, i.e., in darkness, the fluorescence is very easily observed, and with most dyes tested thus far the fluorescence has been very easily observed even in the presence of visible light.

Preferred classes of dye compounds which have been found especially useful as oxygen sensitizers in accordance with this invention are as follows, where X represents an auxochromic group comprising a heavy atom bonded to the chromophore portion of the compound by means of said atom, and n is one or more.

In addition to the OZ and OZ solubilizing groups and the auxochromic groups (designated as X groups), the above classes of dye compounds may also be substituted with various other groups (e.g., fluorine, nitrile, hydroxy, alkyl, aryl, polycyclic, acyl, alkoxy) which are stable and do not cause decomposition of the chromophore portion of the dye compound.

With respect to the preferred classes of dye compounds described above, X preferably represents a heavy halogen atom (e.g., C1 or Br), and preferably n is an integer of at least two.-The X groups can be attached either to the linking moieties or to the moieties comprising the kata condensed aromatic rings.

The dye compounds used in this invention can be prepared by independent synthesis but they are more conveniently prepared from precursor vat dyes containing the anthraquinoid moiety, i.e.,

by first reducing the vat dye in the presence of a strong base. For example, Vat Violet 1 (Color Index No. 60010) may be reduced according to the following scheme to produce the dianion.

NaOH

Ll\ O-Na [la l v The dianion can then be alkylatedwith conventional alkylating agents, e.g.,

scheme. The resulting product has the following formula:

This product may be subsequently reduced via a Wolff- Kischner type reaction to yield a compound of the fol- To form an acyl derivative the vat dye is first reduced where R and R represent stable monovalent organic 20 radicals as described earlier herein.

An example of a reaction scheme which may be used to obtain dyes wherein R and R represent substituted alkyl radicals is as follows. The vat dye is first reduced and acidified to obtain the OH derivative of the vat 25 dye. Then the following reaction is used,

The tetrahydrofuran is removed by distillation and the material is allowed to react with iodobenzene and acti- -v ated copper at an elevated temperature.

according to the description in U. S. Pat. No.

An example of a reaction scheme which may be used to obtain dyes wherein R and R represent substituted phenyl radicals is as follows. Vat Violet l is first reduced in tetrahydrofuran using potassium to obtain the dipotassium derivative as shown The resulting product is the diphenoxy derivative of Vat Violet l. I

The above reaction scheme is also useful for obtaining dye compounds wherein R and R represent polycyclic radicals. For example, when l-iodonaphthalene is reacted with the dipotassium derivative, a dye is obtained having the following formula:

FeCs

C12 heat Other dye compounds within the scope of this invention can also be prepared according to the above reaction schemes. Exemplary halogenated vat dyes which are quite useful as starting materials for the preferred classes of dye compounds used in this invention include Vat Blue 18 (Color Index 59815), Vat Blue 22 (Color Index 59820), Vat Orange 1 (Color Index 59105), Vat Orange 2 (Color Index 59705), Vat Orange 3 (Color Index 59300) and Vat Violet l (Color Index 60010).

The intermediate sheets used in this invention prefe'rably comprise a film-forming binder, acceptor and sensitizer dye in the form of a thin face-coating on a thin light-transmissive film material backingI The facecoating is typically very thin, e.g., from less than 0.1 mil to about 0.5 mil.

Although the amount of sensitizing dye used in the intermediate sheets may be varied over wide ranges, it is preferred to use minimal amounts for economic reasons and so that the light may readily penetrate the dyed coating, although sufficient dye should be used to provide a usefully rapid rate of desensitization of the acceptor under irradiation with visible light from commercially available sources. The amount of sensitizer dye normally used is in the range of about 0.05 to 2 weight percent based on 'the total weight of. the facecoating and is preferably in the' range of about 0.2 to 0.6 weight percent based on the total weight of the face-coating. Mixtures of these polycyclic dyes can be used in the imaging sheets with similar effectiveness.

Mixtures of polycyclic dyes with other known oxygen-' sensitizing dyes can also be used in these sheets,.if desired.-

The amount of acceptor which may be used in the intermediate sheets may vary over wide ranges depending upon the molecular weight and solubility of the particular acceptor used. Normally the amount of acceptor present in the sheet is in the range of about I to 8 weight percent based on the total weight of the face coating, although more or lesser amounts of acceptor may also be used if desired.

Film-forming binders which can be used in this invention include those known in the art, with ethoxylated cellulose derivatives such as Ethocel (N-grade) or Ethocel (T-grade), commercially available from Hercules, being the preferred film-forming binders.

When using the ethoxylated cellulose derivatives as film-forming binders in making imaging sheets in accordance with this invention, it is preferred to use acetone, methyl ethyl ketone, methanol or ethanol, or

combinations thereof, as the major constituents of the solvent system from which the binder, acceptor and dye. are coated. Minor amounts (i.e., less than about 10 weight percent) of other solvents may be included in the solvent system for various reasons, such as presolubilizing the dyes or improving the surface characteristics of the final coating. Such other solvents which may be included in minor amounts include chloroform, -n-butanol, toluene, and heptane.

' The intermediate imaging sheets of this invention can be used with many and various receptor sheets to produce finished copies of originals, so long as the photosensitive acceptor in the intermediate sheet forms a visibly distinct reaction product with a co-reactant present in the receptor sheet. For example, when the photosensitive acceptor is an alpha-naphthol or a substituted hydrazone, suitable co-reactants which are normally used'in the receptor sheet are silver soaps of long-chain fatty acids, e.g., silver behenate and silver stearate. These soaps are visibly stable toward light, are insoluble in many volatile liquid vehicles, and are moisture resistant, and these materials either alone or blended with additional fatty acid are very useful for use in conjunction with the imaging sheets employing alphanaphthol acceptors, although many other readily reducible normally solid organic acid salts of novel metals'ai'e also usefuL-Receptor or imaging sheets employing such co-reactants are described in detail in U.S. Pat. No. 3,218,166 (Reitter), incorporated herein by -reference. Otheruseful receptor sheets are described in U.S. Pat. No. 3,094,417 (Workman). When substituted dithiooxamides are used as photosensitive acceptors, the most commonly used co-reactant is nickel stearate, although other nickel salts can also be used, e.g., nickel acetate. I

Pigments such as zinc oxide, fillers such as powdered silica, resins such as powdered high-melting terpene resin, toning agents such as phthalazinone, and various other modifiers and additives may be included in the receptor sheet if desired.

The amount of organic preservative which is included in the light-sensitive layer of the intermediate sheet material may vary over broad ranges. For example, amounts of about parts of organic preservative for each 100 parts by weight of alpha-naphthol provide improvement in the ability of the intermediate sheet material to resist atmospheric deterioration. Much larger amounts of organic preservative impart further improvement, but quantities much beyond about 800 parts per 100 parts of alpha-naphthol are not ordinarily required and are therefore uneconomical. A preferred range is from about 100 to about 200 parts of the preservative for each 100 parts of the alpha-naphthol.

Preferably the preservative is soluble in the filmforming binder of the light-sensitive layer, and preferably the amine group is a primary amine (NH group. The preservatives may contain more than one amine group. in order to obtain binder-soluble preservatives, these aromatic compounds may contain various solubilizing groups, e.g., alkyl and alkoxy radicals or sulfonic acid groups (or alkaline metal salts thereof). The sodium salt of 4-aminonaphthalene sulfonic acid is a highly preferred organic preservative for use in-this invention. Metanilic acid and sulfanilic acid are also useful organic preservatives, as are the alkaline metal salts of these acids.

The normally non-volatile aromatic compounds which are useful as organic preservatives in this invention exhibit a visible color change or form a precipitate, or both, in the following test, referred to herein as a gaseous nitrogen dioxide test. A 0.1 molar solution of the normally non-volatile aromatic compound is first prepared using a suitable inert solvent. Common solvents used include methanol, acetone, and water, or combinations thereof, although other inert solvents may also be usedso long a the aromatic compound is sufficiently soluble therein to provide an 0.1 molar solution. At room temperature, nitrogen dioxide gas is bubbled through 100 ml. of the 0.1 molar solution of the aromatic amine compound at the rate of 1 liter per hour. Useful aromatic amine'compounds willproduc'e a positive result, Le. a visible color change or formation of a precipitate, or both, within about one minute.

As an example, a solution of the sodium salt of "4- aminonaphthalene sulfonic acid, in methanol, initially exhibits a light tan color but turns to a bright red during the test. If bubbling of the nitrogen dioxide gas is continued, a tan precipitate is obser'ved. As another example, a solution of metanilic acid, in water, initially exhibits a faint yellow color but turns to a bright yellow color during the test. A solution of metanilic acid, in methanol, initially exhibits a faint yellow color but turns to a dark yellowish-orange color during the test.

The reactant or acceptor (e.g. alpha-naphthol), together with the oxygen-sensitizing polycyclic aromatic dye, the organic preservative, and a film-forming binder (e.g., ethyl cellulose), is applied to a thin translucent paper or transparentfilm from solution in a volatile solvent by any desired method of application and the solvent is removed by evaporation, care being. taken to avoid blushing and to produce a uniform compact thin layer. When using organic preservatives which are not readily soluble in the solution of the other ingredients, intensive mixing or homogenizing may be required in order to obtain desired uniformity of the coating mixture.

Example An intermediate film member is prepared by coating formula 00 Use into 4.0 parts by weight of chloroform, the solution then being added to a solution of 7.5 parts by weight n-butanol in 87.7 parts by weight acetone. Ethoxylated cellulose (Ethoce l N-l 00), 4.77 parts by weight, is then dissolved into the solution containing the dye, after which 0.18 part by weight of 4-methoxy-lnaphthol (acceptor) is added. Then 0.09 part by weight of the sodium salt of 4-aminonaphthalene sulfonic acid, in 4.0 parts by weight methanol, is added to the coating solution. The coating solution is coated (0.05 mm. orifice) onto glassine paper in darkness and allowed to dry at room temperature.

The resulting intermediate slieet material is wound in roll form for test, and is compared with a roll similarly prepared except that the organic preservative is omitted. The rolls are placed on copy machines and used in the reflex copy process and are found to produce excellent copies when first tested. However, after prolonged layer including a film-forming binder, an ox ygensensitizing polycyclic aromatic dye, said dye comprising at least two moieties in conjugate relationship as part of a single chromophore, each said moiety comprisingthree linearly kata condensed six-membered aromatic rings, an -OZ group being attached to the meso position of each said moiety, wherein Z is a stable, monovalent radical, said OZ group being a solubilizing group for said compound, wherein at least one auxochromic group comprising an atom having an atomic weight of at least 3] is bonded to saidchromophore by means of said atom, wherein said dye compound exhibits visible flourescense when a 0.001 molar solution thereof isexposed to ultraviolet light in the 200 to 400na'nometer wavelength range; and a reactant which is reactive with a co-reactant to provide a visible change and is rendered non-reactive with said co-reactant upondesensitization with excited oxygen, and further characterized by the inclusion in said lightsensitive layer of a normally non-volatile organic a ro-' reactive with other ingredients in said light-sensitive layer and which gives a positive result in the gaseous nitrogen dioxide test.

2. An intermediate sheet in accordance with claim 1, wherein said reactant is an alpha-naphthol,

3. An intermediate sheet in accordance with claim 2, wherein said organic preservative is selected from the group consisting of metanilic acid, sulfanilic acid, and an alkaline metal salt of 4-aminonaphthalene sulfonic acid.

4. An intermediate sheet in accordance with claim 3, wherein said organic preservative is included in said imaging sheet in an amount between about 100 and about 200 parts by weight for each 100 parts of alphanaphthol.

5. An intermediate sheet in accordance with claim 4, wherein said organic preservative is the sodium salt of 4-aminonaphthalene sulfonic acid.

6. An intermediate sheet in accordance with claim 3, wherein said reactant is 4-methoxy-l-naphthol.

7. A method for preserving, against atmospherically induced deteriorationof light sensitivity, an intermediate sheet of the type comprising a light-sensitive layer including a film-forming binder, an oxygen-sensitizing poly-cyclic aromatic dye, said dye comprising at least two moieties in conjugate relationship as part of a single chromophore, each said moiety comprising three linearly kata condensed six-membered aromatic rings, an OZ group being attached to the meso position of each said moiety, wherein Z is a stable, monovalent radical, said OZ group being a solubilizing group for said compound, wherein at least one auxochromic group comprising an atom having an atomic weight of at least 3] is bonded to said chromophore by means of said atom, wherein said dye compound exhibits visible flourescense when a 0.001 molar solution thereof is exposed to ultraviolet light in the 200 to 400 nanometer wave-length range; and a reactant which is reactive with a co-reactant to provide a visible change and is rendered non-reactive with said co-reactant upon desensitization in said light-sensitive layer a nonnally non-volatile organic aromatic amine preservative essentially non-reactive with the other ingredients in said light-sensitive layer and which gives a positive result in the gaseous nitrogen dioxide test.

8. A method in accordance with claim 7, wherein said reactant is an alpha-naphthol.

9. A method in accordance with claim 8, wherein said organic preservative is selected from the group consisting of metanilic acid, sulfanilic acid, and an alkaline metal salt of 4-aminonaphthalene sulfonic'acid.

UNITED STATES PATENT OFFICE CERTIFICATE OF. CORRECTION Patent No. 3L77 JU D t November 6; 1973 Invento1.'( Leo A; Mever and Robert J PPT'k'I It is certified. thst error appears in the above-identified patent and that "said Letters Patent are hereby corrected as shown below:

Col; 16, Claim 7, line 15, after "desensitization" insert with excited oxygen, the method comprising including Col. 3, line 7, "diphenylisobenezofuran" should read diphenylisobenzoiuran i col. 11, 1ine 30,' in the formula,

FeC FeCl hould read s 01 I v I Y .v 2 C12 I 1 heat Signed and sealed this 9th day of April l97-L L.*

(SEAL) Attest: I

EDWARD M.FLETCHER,JR. 0.. mRsHALL .DANN Attesting Officer v Commissioner of Patents FORM PC4050 10-69) 

2. An intermediate sheet in accordance with claim 1, wherein said reactant is an alpha-naphthol.
 3. An intermediate sheet in accordance with claim 2, wherein said organic preservative is selected from the group consisting of metanilic acid, sulfanilic acid, and an alkaline metal salt of 4-aminonaphthalene sulfonic acid.
 4. An intermediate sheet in accordance with claim 3, wherein said organic preservative is included in said imaging sheet in an amount between about 100 and about 200 parts by weight for each 100 parts of alpha-naphthol.
 5. An intermediate sheet in accordance with claim 4, wherein said organic preservative is the sodium salt of 4-aminonaphthalene sulfonic acid.
 6. An intermediate sheet in accordance with claim 3, wherein said reactant is 4-methoxy-1-naphthol.
 7. A method for preserving, against atmospherically induced deterioration of light sensitivity, an intermediate sheet of the type comprising a light-sensitive layer including a film-forming binder, an oxygen-sensitizing poly-cyclic aromatic dye, said dye comprising at least two moieties in conjugate relationship as part of a single chromophore, each said moiety comprising three linearly kata condensed six-membered aromatic rings, an -OZ group being attached to the meso position of each said moiety, wherein Z is a stable, monovalent radical, said OZ group being a solubilizing group for said compound, wherein at least one auxochromic group comprising an atom having an atomic weight of at least 31 is bonded to said chromophore by means of said atom, wherein said dye compound exhibits visible flourescense when a 0.001 molar solution thereof is exposed to ultraviolet light in the 200 to 400 nanometer wave-length range; and a reactant which is reactive with a co-reactant to provide a visible change and is rendered non-reactive with said co-reactant upon desensitization in said light-sensitive layer a normally non-volatile organic aromatic amine preservative essentially non-reactive with the other ingredients in said light-sensitive layer and which gives a positive result in the gaseous nitrogen dioxide test.
 8. A method in accordance with claim 7, wherein said reactant is an alpha-naphthol.
 9. A method in accordance with claim 8, wherein said organic preservative is selected from the group consisting of metanilic acid, sulfanilic acid, and an alkaline metal salt of 4-aminonaphthalene sulfonic acid. 